In a statement, the city Department of Investigation accused Kuczinski of directing his staff to listen in on calls between the watchdog agency and confidential inmate informants. It said the surveillance continued despite a directive saying it should stop.

The DOI investigates city agencies, officers, officials or employees for potential corruption.

"None of the DOC staff were able to provide a coherent explanation for this misconduct," according to a statement from DOI Commissioner Mark G. Peters. "DOI is particularly concerned that there was a renewal of this activity, directed by Kuczinski, immediately after he and other senior staff were informed that DOI was preparing a report on their improper use of city vehicles."

"Our investigation provided no alternative explanation that would suggest this timing was coincidental," he said.

Peters didn't publicly detail DOI's findings, saying the report contains sensitive information about security operations. But he's made several recommendations to Mayor de Blasio, including re-training DOC staff who are tasked with listening to inmate calls on the proper rules and guidance and overhauling phone monitoring at DOC.

"Interference, by anyone, with a DOI investigation is a very serious matter that will not be tolerated," said Peters. "In particular, surveillance of DOI activities in the city's jails by the very agency DOI is investigating, not only compromises investigations but can potentially put the lives of investigators, correction officers, inmates and others at risk."

While Peters called for Kuczinski to be fired, a City Hall spokesman said he's not been terminated; instead, he was relieved from his investigation and call-monitoring responsibilities.

Mayor de Blasio said in a statement, "These are serious and troubling allegations. We will work with the Department of Correction and the Department of Investigation to determine what happened and what changes must occur to ensure that it doesn't happen again."

There was no immediate response to messages left on Monday for Kuczinski. He has told The New York Times he didn't do anything wrong.

The case is the latest setback for a sprawling jail facility plagued by corruption and violence.

The DOI issued a report last week finding that DOC officials, including Commissioner Joseph Ponte, were using their city-owned cars to take unauthorized personal trips to shopping malls, airports, beaches, spas and resorts last year.